1. Field of the Invention
The present general inventive concept relates to an ink jet head substrate, an ink jet head and method of manufacturing the ink jet head substrate and, more particularly, to an ink jet head substrate provided with a heat-generating resistor having an enhanced reliability and an expanded life span, an ink jet head having the ink jet head substrate, and method of manufacturing the ink jet head substrate.
2. Description of the Related Art
An ink jet recording device is a device for printing a picture by ejecting a minute droplet of printing ink to a desired position of a recording medium. Such an ink jet recording device is widely used because a price thereof is relatively low and various colors can be printed at a high resolution. Typically, the ink jet recording device comprises an ink jet head for ejecting the ink substantially and an ink storage unit for fluidly communicating with the ink jet head. Further, in the ink jet recording device, the ink jet head is divided into a thermal type using an electro-thermal transducer and a piezoelectric type using an electromechanical transducer according to a method of ejecting the ink. A thermal type ink jet recording device has been disclosed in U.S. Pat. Nos. 4,500,895 and 6,336,713.
Such an ink jet head (hereinafter referred to as a thermal ink jet head) used in the thermal type ink jet recording device (hereinafter referred to as a thermal ink jet recording device) generally comprises an ink jet head substrate and a nozzle plate provided with an aperture through which the ink is ejected. In the ink jet head substrate, there is provided an electro-thermal transducer for generating thermal energy to eject the ink. The electro-thermal transducer is generally made of an alloy containing a high melting point metal, such as tantalum (Ta), and will be hereinafter referred to as a heat-generating resistor. Preferably, the heat-generating resistor used in the thermal ink jet head of the thermal ink jet recording device has the following characteristics: (1) basically, it should have a high resistivity, (2) it should be able to reach a required temperature within an extremely short time so as to instantaneously eject the ink, (3) it should have a little variance in resistance so as to keep the droplet of the ejected ink uniform during a high speed operation and consecutive operations, and (4) it should have high endurance against thermal stress so as to expand a life span.
To satisfy the above-described characteristics, a conventional heat-generating resistor has been mostly made of TaAl. The thermal ink jet head employing the heat-generating resistor made of TaAl has been disclosed in U.S. Pat. No. 5,122,812. Meanwhile, the performance of the thermal ink jet recording device can be estimated on the basis of a printing resolution and a printing speed. To improve the printing resolution, there may be proposed a method of decreasing a size of the ejected ink droplet by reducing a size of the heat-generating resistor. In order to operate the thermal ink jet recording device under the same conditions as the conventional one even though the size of the heat generating resistor is reduced, a resistance of the heat-generating resistor should be increased. This can be seen in the followingP/A=V×I/A=I×R2/A=V2/(R×A)  <Equation 1>
where P/A is a power density, A is a area of a heat generating resistor, V is a driving voltage, I is a driving current, and R is a resistance of the heat generating resistor)
Generally, in the thermal ink jet recording device, in order to create a bubble required for ejecting the ink, the power density (P/A) should be over about 1˜2 GW/cm2. Therefore, in order to keep the power density (P/A) constant even though the area (A) of the heat-generating resistor is reduced, the resistance (R) of the heat-generating resistor should be increased. Further, according as the resistance (R) of the heat-generating resistor is increased, the driving current (I) of the thermal ink jet recording device can be decreased, which is advantageous in terms of energy requirement.
However, TaAl used as a material for the conventional heat-generating resistor has a resistivity of about 250˜300 μΩ·cm and a sheet resistance of about 30 Ω/□ (or 30 Ω/square) at about 1000 Å thickness. Thus, there is a limitation in reducing the area of the heat-generating resistor. In order to increase the sheet resistance of the heat-generating resistor, there has been proposed a method of reducing a thickness of the heat-generating resistor, but this method causes the resistance to vary remarkably as the energy applied to the heat-generating resistor is increased, thereby causing the thermal ink jet recording device to be unstably operated.
Consequently, in the conventional thermal ink jet recording device, there is needed to develop the heat-generating resistor having a high resistivity and an enhanced thermal/mechanical endurance to achieve a high printing resolution and a stable high-speed operation. Thus, there have been disclosed a thermal ink jet head comprising a heat-generating resistor made of TaxSiyRz in U.S. Pat. No. 6,527,813, and the ink jet head comprising the heat-generating resistor made of TaN0.8hex in U.S. Pat. No. 6,375,312.